<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box1{
            /* width: 400px;
            height: 400px; */
            /* background: red; */
        }
        .box2{
            width: 200px;
            height: 200px;
            background: royalblue;
            float: left;
        }
        .box1:after{
           content: '';
           clear: both;
           display: block;
           height: 0;
           overflow: hidden;
           visibility: hidden;
        }
                                                                                                          
    </style>
</head>
<body>
    <div class="box1">
        <div class="box2"></div>
        
    </div>
    qqqq
</body>
</html>